1. Field of the Invention
The present invention relates generally to the field of high speed data transfer, and more specifically to managing virtually concatenated payload groups in specific data transfer architectures, such as SONET/SDH.
2. Description of the Related Art
Data communication networks receive and transmit ever increasing amounts of data. Data is transmitted from an originator or requester through a network to a destination, such as a router, switching platform, other network, or application. Along this path may be multiple transfer points, such as hardware routers, that receive data typically in the form of packets or data frames. At each transfer point data must be routed to the next point in the network in a rapid and efficient manner.
Data transmission over fiber optics networks may conform to the SONET and/or SDH standards. SONET and SDH are a set of related standards for synchronous data transmission over fiber optic networks. SONET is short for Synchronous Optical NETwork and SDH is an acronym for Synchronous Digital Hierarchy. SONET is the United States version of the standard published by the American National Standards Institute (ANSI). SDH is the international version of the standard published by the International Telecommunications Union (ITU). As used herein, the SONET/SDH concepts are more fully detailed in various ANSI and ITU standards, including but not limited to the discussion of concatenated payloads, ITU-T G.707 2000, T1.105-2001 (draft), and T1.105.02-1995.
SONET/SDH may employ virtually concatenated payloads. The virtual concatenation payload support for a SONET/SDH network requires compensation for differential delay among members of the same group. Differential delay results from the payload, which is divided into groups, taking different paths through the network, or due to pointer processing, or other considerations. Data generated at the same time from the source node (with the same MFI, multi-frame indication) in the same group may arrive at the destination node at different times. Further, if the network provides LCAS (Link Capacity Adjustment Scheme) support, new payload members may be added or existing members may be removed, again varying the set of arrival times. Data from different members are typically stored in memory upon arrival at the destination node. Differential delay compensation essentially enables processing all virtual concatenation payload groups at the destination node at one time. In other words, the destination node reads all data from members having the same MFI at one time.
The SONET/SDH virtual concatenation standard provides a maximum differential delay equal to 2048 frames or 256 ms. Differential delay beyond this value cannot be processed. Actual compensable differential delay depends on the memory size used to store the data, called the Alignment Buffer. Alignment Buffer specifications are provided in ITU-T G.783, and state that the LOA (Loss of Alignment) defect “shall be detected if the alignment process cannot perform the alignment of the individual VC-4s to a common multiframe start (e.g. dLOA [LOA defect] is activated if the differential delay exceeds the size of the alignment buffer.)” LOA defect generation is not specified, and may take various forms depending on circumstances.
A design for loss of alignment defect (dLOA) signal generation, applicable when the alignment process in a virtually concatenated environment employing differential delay compensation when the differential delay exceeds the size of the alignment buffer, may provide enhanced processing capabilities and other advantageous qualities over previously known designs, including designs employing the SONET/SDH architecture.